1. Field of the Invention
The present invention relates to a navigation system and a navigation apparatus used in the navigation system, in which data concerning a recommended route from the current position of the navigation apparatus on a vehicle to the destination thereof is transmitted from a navigation center to the navigation apparatus by means of communications, with the navigation apparatus then providing route guidance for the recommended route to a user using such received data.
2. Description of the Prior Art
At present, navigation apparatuses which provide route guidance for a travel route to a destination to a user are widely used. In these navigation apparatuses, each apparatus is equipped with navigation data such as data related to destinations (targets of guidance), road data for performing a search for a recommended travel route to a destination, and map data for producing display images and the like. Further, each navigation apparatus is provided with a GPS receiver or the like for detecting the current position of the vehicle. In such navigation apparatuses, a recommended route from the current position to the destination is determined using road data, and route guidance along the recommended route is carried out with indicating the current position of the vehicle and the travel directions (going straight or turning left or right etc) on the displayed recommended route.
Further, in addition to the navigation apparatuses described above, a communications navigation system is developed. In this type of navigation apparatus, the current position of the vehicle is detected at the navigation apparatus in the vehicle, while search for a recommended route to the destination is carried out at a separate information center or the like. The navigation apparatus receives the data concerning the recommended route from the information center to perform the route guidance using the received data and the like.
An example of this type of navigation system is disclosed in Japanese Laid-Open Patent Publication No. HEI 10-160497, in which a travel route is determined using recommended route data transmitted from outside the vehicle such as the information center described above. Specifically, in this navigation system, the information center navigation apparatus sends data of a recommended route in the form of a string of link numbers to a navigation apparatus, and then the navigation apparatus converts the received string of link numbers into a string of link numbers for the navigation apparatus, and then a travel route to the destination is established in the navigation apparatus using the string of the converted link numbers.
However, in this navigation system, there is a case that the navigation apparatus receives, as data for a recommended route, a string of link numbers of intersections or roads (e.g., newly constructed intersections or roads) of which data is not stored in the storage medium in the navigation apparatus. In such a case, it is not possible for the navigation apparatus on the vehicle to identify the intersection or road represented by the string of link numbers, which results in a problem in that rout guidance can not be carried out at the navigation apparatus even though the data for the recommended route has been duly received from the information center.